This invention relates to internal batch mixing machines having a mixing chamber and a driving mechanism which causes a pair of rotors to rotate in opposite directions to mix materials and relates to the structure of rotors for use in these machines.
In internal batch mixing machines, a batch of materials to be mixed into a homogeneous mass is fed into a mixing chamber through a vertical chute and is pushed down into the mixing chamber under pressure by a ram located in the chute. This ram may be driven hydraulically or pneumatically or by any other convenient type of mechanism. When the ram is moved down to its operating position during the mixing of a batch of ingredients, the lower face of the ram forms an upper closure of the mixing chamber. The mixture of ingredients which is produced can be removed from the mixing chamber by opening a door to a discharge opening at the bottom of the chamber. The door is then closed prior to introducing the next batch of materials into the mixing chamber.
Internal batch mixing machines mix materials through the use of a pair of rotors which are rotated in opposite directions from one another as a batch of materials are mixed. The rotors are rotated by a drive system which includes a motor, a gear mechanism for connecting the motor to the rotors and controls for stopping, starting, and controlling the speed of the motor. Each of the rotors has a drive end connected to the drive system and coolant or water end through which coolant such as water is circulated through the rotors. Each of these rotors has a plurality of lobes, that is, extensions or protusions of the rotor beyond its smallest or minor diameter, which mix the materials. The lobes may be wings, that is elongated extensions having generally narrow top surfaces along their lengths.
This invention relates to internal batch mixing machines that include rotors of either an intermeshing or a non-intermeshing type. Intermeshing rotors are constructed and installed within these machines so that the lobes of one rotor fit into spaces between or within the lobes of the other rotor. Non-intermeshing rotors are constructed and installed so that the ends or the major diameter of the lobes of one rotor do not rotate into the space within which the lobes of the other rotor rotate. In an internal batch mixing machine, intermeshing rotors must always be driven at the same rotational speed in synchronized relationship with one another. Non-intermeshing rotors may each be driven at the same rotational speed or they may be driven at different rotational speeds, sometimes called the friction ratio operating mode, for achieving different effects with respect to a batch of ingredients.
Internal batch mixing machines are well known for mixing polymer materials such as rubber. One of the earliest of these machines is shown in U.S. Pat. No. 1,200,070, issued in 1916. While there have been many different internal batch mixing machines based on different rotor designs, there is a continuing need to provide internal batch mixing machines, including rotors used in these machines, to more intensively mix the materials put into them, more rapidly reach a homogeneous mass and thus increase the productivity of these machines.
The internal batch mixing machine of this invention includes a housing having a mixing chamber located within it which is shaped to have a first rotor and a second rotor mounted on parallel, horizontal axes. The housing includes an inlet for receiving materials to be mixed within the mixing chamber and an outlet for discharging mixed materials from the mixing chamber. The mixing machine also includes a drive system which can rotate the two rotors in opposite directions within the mixing chamber.
Each of the two rotors has an axis of rotation, a first axial end and a second axial end. One of these ends is connected to the drive system and is called the drive end and the other end receives coolant for the rotors and is sometimes called the coolant end. When the rotors are installed in the mixing machine, the first axial ends of both of the rotors are adjacent one another, and the second axial ends of both of the rotors are adjacent one another. The circumference of each rotor is divided into first, second, third and fourth sequential quadrants which are spaced in a direction opposite to the intended direction of rotation of that rotor. In the preferred embodiment of this invention each of these four quadrants will occupy 90xc2x0 of the circumference of the rotor. However, the quadrants may be of any size desirable for a particular application of this invention.
In accordance with one aspect of this invention, each of the rotors can have a separate pair of lobes located in every other quadrant of the rotor. Each lobe has a leading end and a trailing end. In this configuration of this invention, the first rotor has a pair of lobes in each of its first and third quadrants, while the second rotor has a pair of lobes in each of its second and fourth quadrants. One of the lobes of each pair of lobes is longer than the other. In other configurations of this invention, the first rotor has a pair of lobes in one of the first and third quadrants and at least a longer lobe in the other, and the second rotor has a pair of lobes in one of the second and fourth quadrants and at least a longer lobe in the other. In the preferred embodiment of this invention each of the pairs of lobes has one lobe with its leading end at one axial end of the rotor on which it is located and the other lobe with its leading end at the other axial end of that rotor. It is preferable to have the leading ends of the longer lobes in the first quadrant and in the third quadrant of the first rotor located at opposite axial ends of the first rotor. It does not matter which of the longer lobes originates on the drive end of the first rotor and which of the longer lobes originates on the coolant end. However, in accordance with the preferred embodiment of this invention significant benefits in mixing will be attained even if both of the longer lobes originates at the same end of the first rotor.
But no matter which configuration of lobes is used on the first rotor in the preferred embodiment of this invention, the longer lobes in the second and fourth quadrants of the second rotor may have their leading ends, respectively, at the axial ends of the second rotor which are opposite from the axial ends at which the longer lobes in the first and third quadrant have their leading ends. Each of the lobes on both rotors extends in a direction opposite to the intended direction of rotation of the rotor on which it is located at an acute angle with respect to a line through its leading end which is parallel to the axis of rotation of that rotor.
In further accordance with this invention, the lobes of each pair of lobes have respective lengths, locations of origin within the rotor quadrant in which they are located and acute cohelix angles at which they extend to cause material adjacent the longer of the lobes of each pair of lobes to be pushed away from the axial end of the rotor at which its leading end is located and toward the other axial end of that rotor, and to form a space between the trailing ends of each pair of lobes at which material flowing adjacent both of each pair of lobes become confluent, with the space formed between the trailing ends having a size which causes the confluent material to be squeezed between the trailing ends of both lobes of each pair of lobes and to flow out of the space between the trailing ends of both of the lobes. As a result, as each quadrant of each rotor which has a pair of lobes within it rotates, material being mixed is released through the space between the trailing ends of each pair of lobes after it has been squeezed, adding a turbulence to further mix the material as it flows from one axial end of the rotors to the other.
In accordance with another embodiment of this invention, the leading ends of the long lobes of each rotor may be located near rather than at opposite axial ends of the rotor. In this embodiment of the invention, the axial length of each short lobe should be longer than the length of the space between the leading end of each long lobe and the axial end of the rotor which that leading end is near. Each short lobe deflects material which passes between the leading end of a long lobe and the axial end of the rotor that leading end is near toward the space where material is squeezed and released.
While the preferred embodiment of this invention utilizes intermeshing rotors each housing a separate pair of lobes in every other quadrant as described above, this invention contemplates other rotor configurations, as well. For example, an internal batch mixing machine can be constructed according to the principles of this invention by eliminating a short lobe from one of the quadrants of one or both of the rotors. As a result, one or both of the rotors will have only three lobes located on it, two of which will be a pair of lobes in one quadrant of the rotor which are constructed in accordance with the principles of this invention. Furthermore, any configuration of rotors constructed in accordance with the principles of this invention can be used as non-intermeshing rotors as well as in an intermeshing arrangement.
Thus, this invention does not reside in any one of the features of the internal batch mixers and rotors which are disclosed above and in the Description of the Preferred Embodiments and claimed below. Rather, this invention is distinguished from the prior art by its particular combination of features of the internal batch mixers and rotors disclosed. Important features of this invention have been disclosed in the Detailed Description of the Preferred Embodiments of this invention which are shown and described below, to illustrate the best mode contemplated to date of carrying out this invention.
Those skilled in the art will realize that this invention is capable of embodiments which are different from those shown, and the details of the structure of the internal batch mixers and rotors can be changed in various manners without departing from the scope of this invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and are not to restrict the scope of this invention. Thus, the claims are to be regarded as including such equivalent internal batch mixers and rotors as do not depart from the spirit and scope of this invention.